Leetcode•Apr 28, 2026

Design HashMap

Hazrat Ali

Leetcode

Design a HashMap without using any built-in hash table libraries.

Implement the MyHashMap class:

  • MyHashMap() initializes the object with an empty map.
  • void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
  • int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
  • void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.

 

Example 1:

Input
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]

Explanation
MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1);    // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3);    // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2);    // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2);    // return -1 (i.e., not found), The map is now [[1,1]]

Solution
class MyHashMap {
    constructor() {
        this.size = 1000;
        this.buckets = Array.from({ length: this.size }, () => []);
    }

    hash(key) {
        return key % this.size;
    }

    put(key, value) {
        let index = this.hash(key);
        let bucket = this.buckets[index];

        for (let pair of bucket) {
            if (pair[0] === key) {
                pair[1] = value;
                return;
            }
        }

        bucket.push([key, value]);
    }

    get(key) {
        let index = this.hash(key);
        let bucket = this.buckets[index];

        for (let pair of bucket) {
            if (pair[0] === key) {
                return pair[1];
            }
        }

        return -1;
    }

    remove(key) {
        let index = this.hash(key);
        let bucket = this.buckets[index];

        for (let i = 0; i < bucket.length; i++) {
            if (bucket[i][0] === key) {
                bucket.splice(i, 1);
                return;
            }
        }
    }
}


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